Process for plating metal on iron or steel by application of a cold solution of a salt of the metal



Patented Aug. 2, 1949 PROCESS FOR PLATING METAL ON IRON OR STEEL BY APPLICATION OF A COLD SOLU- TION OF A SALT OF THE Arthur Arent, Fort Dodge, Iowa, assignor 'to Arthur Arent Laboratories, Inc.,'Des Iowa, a corporation of Iowa Moines,

No Drawing. Application January 16, 1945, Serial No. 573,145

This invention relates to the art of surfacecoating metals and metallic objects and more particularly relates to the application of surfaces or'finishes to metallic objects which are of a different composition than the metal to which they are applied.

Industrial uses of irons and steels have become so widespread and diversified that there is a continual demand for new properties in such metals. Likewise, the new uses frequently require new surfaces or finishes on articles or objects fabricated from iron and steel. For example, the steel industry has long sought a satisfactory way to put. lead on steel and bond it tightly enough to withstand subsequent fabrication operations without flaking off or loosening.

It is an object of the present invention to provide a simple, economical and efficient method of surface coating or finishing metallic surfaces, particularly steel and iron surfaces, to enhance their appearance'and render them substantially rust or corrosion resistant.

Another object of this invention is to produce steel objects or articles having an iron-containing surface of different composition than the composition of the steeL.

A further object'of my invention is to provide a process for bonding metallic surfaces on steel or iron by cold immersion or brush application methods.

Still another object of this invention is to provide steel objects having a lead surface coat tenaciously bonded therewith.

' A still further object of this invention is to provide a simple, efficient and economical process for plating zinc or galvanized iron surfaces by application of a cold solution thereto.

Other objects reside in novel combinations of materials and in the provision of novel steps and treatments, all of which will be described in the course of the following description.

Briefly stated, the present invention resides in the discovery that by applying citric acid or a metal citrate in citric acid solution to the exposed surfaces of iron or steel objects, a surface reaction can be obtained which renders said surface substantially rust-resistant and imparts a bright silvery lustre thereto The practice of the present invention will be best understood by citing certain typical examples of the procedure to be followed. In the first of these, it was desired to apply a rustresistant coating to sheet steel. This steel was originally washed with suitable solution to remove any adhering grease, and then was cleaned 5 Claims. (01. 148-614) 2 with commercial muriatic acid to remove any adhering rust.

Following application of the muriatic acid, the steel was washed thoroughly with water. Care should be exercised not to use an alkaline wash to neutralize the acid as to do so will seriously impair the efficiency of the subsequent treatment. After rinsing the steel it should be dried, either by natural or artificial methods, and as soon as dried, the steel should be passed on immediately to the next treatment stage.

At the next stage citric acid is applied to the surface for the steel, preferably by brush, or'by spraying or immersion if desired, and this surface application should ;be continued from one to three minutes. The strength of the solution may be varied to a considerable extent and preferably should be from 25% to concentrated. However, in treating steel surfaces best results have been obtained with a concentrated solution. The solution may be maintained at room temperature in the treatment, and no'external electric current is required in obtaining the surface coating.

After applying the citric acid solution, the steel is washed with water and dried. Upon completion of this treatment the steel has a bright silvery surface appearance and possesses a high degree 'of resistance to corrosive influences. From tests conducted, the application of the muriatic acid apparently induces surface changes which bring previously unexposed steel to the surface, which at the time of 'exposure apparently has not undergone any surface oxidation. This surface is believed to contain a quantity of iron citrate, which while closely bonded with the steel is of substantially different composition and therefore has different properties, particularly in its resistance to corrosion.

For certain purposes it is desirable to surface coat steel with another metal to give, in effect, the properties of the second metal to the steel. For example, the steel industry has long sought a practical method of bonding metallic lead on steel surfaces to make them acid and corrosion resistant. The present process provides a practical solution to this problem.

In lead coating operations the steel surface is prepared for treatment by repeating the aforesaid operation. After the surface is washed and dried following the first application of the citric acid solution, the surface is again treated by brushing on, spraying on or immersing in a citric acid solution in which lead or a lead salt has been dissolved. This treatment continues for from one to three minutes, after which the coated surface is washed and then dried.

The thickness of the coating or plating so applied is variable depending on the concentration of the lead-in.-so1ution-=and the duration of the treatment. .On completion of thetrea'tment, the new surface has the distinct appearance and other characteristics of the lead which it contains.

Another procedure which may be utilized to give the steel or iron a preliminarycleaning, followed by immersion in or surface wetting with a citric acid solution contai g :a-meta-l, such as copper, lead or zinc. The :citric .acid zacts on the steel or iron to cause a surface change'as aforementioned, and the metal in solution .deposits onto and bonds with the materialin the changed surface.

From the foregoing description, it will be apparent that the methods of the present invention rare economical as they require only a'brief treatment interval and no heating or electric-current in applying the plate or surface coat to the metal objects. These plates are :bonded sufiiciently to -.vr-ithstand subsequent fabricating operations without loosening, and are effective in giving Trista-resistant :and -;other properties to the metal.

AMI-K181337431 metals are amenable to the present treatment. 'In generaLany metallic-iebieet that will enter into surface-reaction with citric acid may :be surface-coated by these methods. Iron, steel, galvanized or mine "surfaces in particular, will be benefited by suchtreatments. A. variety .of-compositions may be utilized in forming the plate -or surface coat. In general, it 'may be stated thatany metal or metallic salt that forms .a metal citrate may be usedfor this purpose, and more particularly iron, copper, lead-and antimony are cited as metals-suited for such uses.

In all the rinsing operations of the aforesaid methods, it'is preferable to use water as the rinsing solution. It is unnecessary at anytime to use alkaline neutralization as better results have been obtained in each instance where the water rinse was used.

What 'I claim and .desire to secure by Letters Patent is:

1. The process for renderingferrous metal surfaces resistant -to corrosion which includes the steps of wetting the surface of the metal with muria-tic acid, washing the surface withwater to remove the acid, and subsequently subjecting the washed surface to the action ofcitric acid, said acid havinga concentration of not less than 2. Theprocess for treating ferrous metal surfaces which includes the steps of first wetting group consisting of copper, lead,

the surface of the metal to be treated with a mineral acid, washing the surface with water to remove the acid, and subsequently subjecting the surface to the action of an aqueous solution consisting :substa-ntially of "citric acid containing a dissolved lead salt, the concentration of the acid being not less than 25%.

3. The process for treating ferrous metal surfaces which comprises the steps of first, wetting the surface to be treated with a mineral acid, then washing the surface with water until free of the acid, and subsequently subjecting the washed surface to lthe action of an aqueous solution consisting of citric acid having a concentration of not less than 25%, and a dissolved metal of the zinc and I antimony.

4. The process for treating ferrous metal surfaces to render said surfaces resistant to corrosion which includes the steps of first, wetting the surfaceof the metal :muriatic 'acid, washing the surface with water to remove rt-he acid, and subsequently subjecting the washed surface to the :action of anraqueous solutionof citric acid containing not less than.2'5t% citric acid, said solution also containing a salt tof as :metal selected from a class consisting of dead, copper, and zinc.

5.- The process for treating ferrous metaLlzsurfaces which includes the steps of wettingit'hesurface with muriatic acid, Washing the surface with water to remove the acid, subjecting :the :washed surface to the action of an'aqueous solution of citric acid having 'a concentration of not less than twenty-five per cent, and subsequent-lyesubjecting the surface to the action of :an aqueous solution consisting substantially of .citric acid having a concentration of not less than'twen tyfive percent and a dissolved leadsalt.

REFERENCES CITED The following referenlces are of record in the file of this patent:

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